Para-oriented aromatic polyamide filaments have an excellent dynamic performance and thus are widely used as industrial filaments for various uses. However, the p-type aromatic polyamide filaments have a disadvantage in that when twisted, the resultant twisted filament yarn exhibits a poor utilization of tenacity and this tenacity utilization significantly decreases with an increase in the twist number thereof. Therefore, the excellent dynamic performance, for example, the high tenacity of the aromatic polyamide filament yarns is not sufficiently utilized for practical use because of poor utilization of the tenacity and poor resistance to fatigue. The main reasons for the above-mentioned disadvantages have not yet been made sufficiently clear. Nevertheless, it is assumed for the main reasons that since the aromatic polyamide filaments have a relatively low stretchability, a large stress derived from the deformation of the filaments when twisted, is created; since the high molecular chains are hard, the filaments exhibit a high rigidity modulus; and the surface friction between the filaments which is a surface property of the filaments is high.
Accordingly, to develop the utilization of cords having a high twist number in a practical use in which a high impact strength is required, there is a strong demand for aromatic polyamide filaments having a high utilization of tenacity thereof even when twisted.
In conventional means for enhancing the tenacity of the twisted aromatic polyamide filament yarns, an attempt was made to reduce the friction between the filaments by applying a surface treatment, an oiling agent or a surface coating to the filaments.
It is known that the tenacity utilization of the twisted filament yarns can be slightly enhanced by controlling the composition, application procedures and amounts of the oiling agent as disclosed in Japanese Unexamined Patent Publication (Kokai) No. 2-216,276. However, the processability and workability including a rubber-adhering property, of the resultant products have not yet reached a satisfactory level.
Also, an attempt to adhere true spherical particles having a low friction to the surfaces of the filaments was made by Japanese Patent Application No. 3-191213. In this attempt, the durability of the product is not reliable. Therefore, the means for reducing the friction between the filaments by the surface treatment are not successful at the present.